The present invention relates to a device and to a method for joining together rod-like elements.
The invention also relates to a piston pump.
It is often necessary to join together rod-like elements. In many instances, all that is required is to obtain a rod-like element whose length has been extended both effectively and reliably. In other instances, there is required a joint which will enable a load, or force, to be transferred through the joint and between the rod-like elements joined thereby. Joining of rotating rod-like elements or shafts is an example of this latter case, as is also joining rod-like elements where linear motion shall be transferred between the rod-like elements, e.g. an impact movement. One example of when rod-like elements are joined, or spliced, together and linear movement is required is found in linear motors used to drive various types of machine where uniform reciprocating movement is required with rapid changes in the direction of movement. A double-acting piston pump is one example of such a machine. Double-acting piston pumps are used for pumping different liquids, which may contain solid particles and which are more or less viscous. Examples of areas of use in this latter case are pumping mud and water slurries in different types of ground drill holes, injecting cement and sand into rock, for instance in tunnel driving operations or in the building of power station dams. A piston pump must be able to handle relatively high pressures and must be possible to regulate the pressure and rate of flow in the pump. Furthermore, the piston pump must be reliable in operation, even when the pumped liquid contains particles, for instance comprised of cement and sand or recycled mud that contains drills"" cuttings.
In the case of known techniques of establishing a joint between the piston rod-like element of the linear motor and the piston rod-like element of the pump, one of the rod-like elements is provided with an internal thread and the other rod-like element is provided with an external thread and the joint is established by screwing one rod-like element into the other. When this type of joint is used in respect of piston rod-like elements in cement injection pumps, cement will sometimes become baked in and around the pump components, therewith making it difficult to unscrew the rod-like elements and separate the pump from the linear motor. The rod-like elements normally have a small size, in the order of 20-50 mm which causes particular problems. One problem in particular is that the thickness of the material is too small to provide a strong joint, and the threads often give rise to fatigue fractures. Another problem, which is quite usual, is that sand and dirt enter between the threads and therewith lock the screw joint.
The object of the present invention is to provide a method and a device which solves the aforesaid problems and which provides a simpler and more secure rod-like element joint in general and a joint between linear-motor piston rod-like elements and piston pumps in particular.
In accordance with the present invention, a device for joining or splicing together two rod-like element-like elements of which each have at least one end that is to be spliced with a respective end of the other rod-like element and which ends are placed so as to face towards each other and to lie adjacent one another, wherein the device includes an inner sleeve where the distance from the centre of the sleeve to its outer wall decreases in the longitudinal direction of the sleeve, at least along a part of the extension of said sleeve in said longitudinal direction, wherein the inner sleeve is designed to be brought externally over the mutually facing ends of said rod-like elements, wherein the device further includes an outer sleeve where the distance from the centre of the sleeve to the internal wall thereof decreases in the longitudinal direction of the sleeve, at least along a part of the extension of said sleeve in said longitudinal direction, wherein the outer sleeve is designed to be brought externally over the inner sleeve, wherein the outer side of the inner sleeve and the inner side of the outer sleeve are designed to be joined together in a shape-bound manner, wherein the device further includes means for locking the two sleeves relative to one another, and connecting means for lockingly joining the inner sleeve to respective rod-like element ends, wherein the connecting means include recesses and projections which are adapted to connect the inner sleeve with respective rod-like element ends in a shape-bound manner, wherein the recesses have inner sloping abutment sides and the projections have corresponding outer sloping abutment sides, and wherein said inner and outer sloping abutment sides are adapted to lie in mutual abutment such as to provide said connection.
This device provides the advantage of a plain connection, meaning a threadless connection, which is much stronger mechanically than known joints, among other things because joint locking and fatigue fractures are avoided, therewith resulting in a longer useful life, improved economy and generally simpler service. In addition, better force transmission is obtained with the inventive join, since the whole of the splicing device is stiffer, more robust, than known devices. A particular advantage is that a clearance-free connection for axial force transmission is obtained. The device and the elements provided on the ends of the rod-like elements or like elements and forming part of said device are locked in relation to each other in an axial direction.
As before mentioned, the recesses have inner, sloping sides (alternatively they can be described as inclined, angled or conical sides) and the projections have corresponding outer, sloping sides. The inner and outer sloping sides are configured to lie in mutual abutment such as to provide said connection. This implies that the recesses and projections will normally have a general V-shape, although preferably not with a pointed bottom, in other words a shape in which the pointed part of the V has been removed. The top of the projection will also conveniently have a planar surface, which is adapted so as not to reach the bottom of the recess/groove. In this respect, the bottom of the groove may be given a small radius, therewith reducing the danger of fatigue and improving the mechanical strength of the groove. It is also preferred that the sleeve will not abut the outside of the rod-like element and that abutment between the sleeve and the outside of respective rod-like elements will only occur through the medium of the sloping sides of the recesses and projections respectively. These design details are mutually coactive in ensuring contact between the sloping surfaces in the recesses and on the projections, therewith resulting in the advantage of a rigid joint or splice.
In accordance with a particularly beneficial feature and in accordance with the foregoing, the device includes a small clearance between the internal axially extending surface of the inner sleeve and the externally and axially extending surface of the ends of respective rod-like elements, so that abutment between the inner sleeve and respective ends of said rod-like elements can only be achieved through the medium of said sloping abutment sides of respective projections and recesses.
Another beneficial feature of the invention is that the two sleeves are locked relative to one another by means of a wedging action.
In one preferred embodiment, a small clearance remains between the ends of the rod-like elements when said rod-like elements are in position in the inner sleeve of the rod-like element-splicing device. This clearance will preferably be in the order of 0.5-0.8 mm. The advantage with this clearance is that forces will not be transferred between the spliced ends of the rod-like elements per se, but via the sleeves.
The inventive method is characterized in that in the event of linear movement between the spliced rod-like elements, the forces involved are transmitted, or transferred, via the sloping abutment surfaces provided on the inside of the inner sleeve and the corresponding sloping abutment surfaces provided on the outside of respective rod-like element-ends, these mutually abutting surfaces providing a shape-bound connection. According to a further beneficial feature of the invention, the inner sleeve and the rod-like element-ends are locked relative to one another in the axial direction.
According to a first embodiment, the connecting devices included recesses that extend circumferentially around the rod-like elements to the joined, close to their respective ends, wherein the connecting devices are further characterized in that they include projections on the inside of the inner sleeve, said projections and recesses being adapted to provide a shape-bound connection. According to an alternative embodiment, the connection devices include projections on the circumferential surface of respective rod-like elements, close to respective ends of said rod-like elements, and recesses on the inside of the inner sleeve, said projections and recesses being adapted to provide a shape-bound connection. The projections will conveniently have the form of projections that extend transversely to the longitudinal axis of the inner sleeve and which also extend inwardly within the inner sleeve. Alternatively, the projections may extend transversely to the longitudinal axis of respective rod-like elements on respective rod-like element ends. The projections will conveniently have the form of radial projections. The recesses will preferably have the form of grooves that extend transversely to the longitudinal direction of the inner sleeve and respective rod-like elements. The grooves, or recesses, will conveniently be radial grooves. The internal geometrical design of the rod-like elements and the inner sleeve must, of course, be mutually adapted. Thus, it is not necessary for the rod-like elements to have a circular cross-sectional shape, and neither is it necessary for the interior of the inner sleeve to have a circular cross-section, but may have a rectangular cross-section, for instance.
In one particularly preferred embodiment, the inner sleeve is divided into at least two parts, preferably two halves. This enables the inner sleeve to be fitted readily over the join ends and also contributes in achieving positive contact between the sloping surfaces of the recesses and of the projections, in the same way as that described above.
Locking of the two sleeves, which thus lie in abutment with one another, is achieved with the aid of locking means which, in turn, conveniently include a counterpressure element adapted for abutment with that end of the inner sleeve at which the distance from the centre of the sleeve to its outer wall is greatest. The locking means also include a locking element on the outer sleeve, said locking element conveniently including a perforated flange. The counterpressure element also includes a perforated flange and the locking means also includes screws that are screwed into said holes, so as to form a screw joint, which constitutes said locking means. Tightening of the screws will thus draw, the counterpressure element into contact with the outer sleeve while, at the same time, pressing the inner sleeve in one direction as the outer sleeve is acted upon by the screw tension in the opposite direction, therewith achieving an effective wedging action between the two sleeves. The inner sleeve is conveniently configured so as to have a generally conical outer surface, and the outer sleeve is conveniently configured so as to have a generally conical inner surface, said surfaces being configured for shape-bound coaction.
Naturally, respective outer surfaces and inner surfaces may have some other configuration, for instance a rectangular or triangular cross-sectional shape. Finally, in respect of the screw joint, the outer surface of the outer sleeve may have any suitable form. The number of screws required may vary, as desired. Neither is there any necessary relationship between the internal and external shape of respective sleeves.
As before mentioned, the invention is particular suitable for application with a piston pump. The piston pump will be of a kind that preferably includes a cylinder that has a front and a rear cylinder wall, and a piston that is reciprocatingly moveable in the cylinder and fastened to a piston rod that passes through one of the cylinder walls, and a linear motor that has an outwardly extending rod-like element for driving the piston pump. The piston rod of the piston pump is spliced, or joined, to the outwardly extending rod-like element of the linear motor by means of the inventive device described afore.